The present invention generally relates to copying apparatuses and more particularly, to an electrophotographic copying apparatus enabling duplex copying and composite copying.
Recently, copying apparatuses having various functions have been developed. Such functions include duplex copying in which copying is performed on opposite faces of each copy paper sheet and composite copying in which different images, for example a frame and characters in the frame are copied onto one face of each copy paper sheet by using different colors. In order to perform the functions of this kind, it is necessary to temporarily transport onto an intermediate tray the copy paper sheet having subjected to initial copying and then, refeed the copy paper sheet. In the case of duplex copying, the copy paper sheet is required to be turned over.
Thus, firstly, an arrangement was proposed in, for example U.S. Pat. No. 4,162,844 in which a feed passage changeover device is provided at an outlet of a fixing device and, at the time of duplex copying, the copying paper sheet discharged from the fixing device is temporarily transported into an upper turnover feed passage so as to be conveyed, through so-called switchback thereof, onto the intermediate tray in a turnover state.
However, in the known switchback method referred to above, since the turnover feed passage of the copy paper sheet is required to be provided at right angles to a transport passage of the copy paper sheet, such problems arise that space efficiency in the copying apparatus becomes deteriorated and copying speed drops due to loss in time for transporting the copy paper sheet. Furthermore, the known arrangement is disadvantageous in that since the turnover feed passage is incorporated in the copying apparatus, it is quite troublesome to remove a jammed copy paper sheet if jamming of the copy paper sheet takes place at the turnover feed passage.
Secondly, in the prior art copying apparatuses, the copy paper sheet may be readily curled due to heat of fixing of a toner image on the copy paper sheet, which fixing is performed by the fixing device before the copy paper sheet is transported onto the intermediate tray. Especially, when a number of the upwardly curled copy paper sheets are stacked on the intermediate tray, height of the copy paper sheets on the intermediate tray becomes large. If the copy paper sheets are aligned with each other on the intermediate tray in this state, regulating plates for regulating leading and trailing edges of each copy paper sheet are required to be made large in height, so that space for the intermediate tray increases, thereby making the copying apparatus itself large in size.
Thirdly, in the known copying apparatuses, in the case an arrangement is employed in which the copy paper sheet is turned over immediately before being transported onto the intermediate tray, diameters of turnover transport rollers for turning over the copy paper sheet should be taken into consideration in connection with space of the arrangement. Furthermore, in the arrangement, it is necessary to positively turn over a hard copy paper sheet like a board, a soft copy paper sheet like a thin paper and a curled copy paper sheet. On the other hand, it is preferable that the copy paper sheet is turned over at as large a radius as possible such that improper turnover of the copy paper sheet is minimized. However, if the turnover radius is made excessively large, the copying apparatus becomes large in size undesirably.
Fourthly, in the known copying apparatuses, a refeeding means is required to be retracted upwardly when the copy paper sheet is transported onto the intermediate tray. Furthermore, the copy paper sheet may be readily curled due to heat of fixing the toner image on the copy paper sheet, which fixing is performed by the fixing device before the copy paper sheet is transported onto the intermediate tray. Especially, in the case where the opposite lengthwise sides of the copy paper sheet are curled upwardly in a widthwise direction of the copy paper sheet, such a problem is incurred unless the copy paper sheet is depressed from above by any guide means that opposite lengthwise side portions of the copy paper sheet are not guided by side regulating plates, thereby resulting in improper refeeding of the copy paper sheet, e.g. oblique refeeding of the copy paper sheet.